What causes colon cancer?

There is rarely one identifiable cause in an individual. Risk reflects a combination of age, inherited susceptibility, bowel conditions, lifestyle exposures and chance changes that accumulate in cells.

Many colon cancers begin in the lining of the bowel, sometimes within a growth called a polyp. Some polyps remain harmless, while others can collect cellular changes over time and become cancerous.

Risk may be higher with a close family history of colorectal cancer or certain polyps, an inherited cancer syndrome, or long-standing inflammatory bowel disease. Smoking, alcohol use, limited physical activity, excess body weight and a diet high in processed meat may also contribute. Having a risk factor does not mean cancer will develop, and people without obvious risk factors can still be diagnosed.

Tell your clinician about colorectal cancer, advanced polyps and related cancers in close relatives, including the relative's age at diagnosis. This can influence when screening begins and whether genetic counselling is appropriate.

Attend recommended bowel screening, avoid tobacco, limit alcohol, stay physically active and favour meals built around vegetables, fruit, whole grains and other fibre-rich foods. These choices can support bowel and general health, but they cannot remove every cause of colon cancer.

Arrange a medical assessment for persistent blood in the stool, an unexplained change in bowel habits, ongoing abdominal discomfort, unexplained weight loss or unusual tiredness. Colon cancer can present with these symptoms, but they also have many non-cancer causes that need proper assessment.

Seek urgent care for heavy rectal bleeding, fainting, severe or worsening abdominal pain, repeated vomiting, or a swollen abdomen with inability to pass stool or gas. These features can signal significant bleeding or bowel obstruction.

Ask whether your family history changes your screening plan, whether previous polyps affect follow-up, and whether inflammatory bowel disease warrants a tailored surveillance schedule. If several relatives had related cancers, ask whether a genetics referral could clarify inherited risk.